A process for the preparation of silicone/vinyl block copolymers starting from linear polysiloxane(azobiscyanopentanamide) macroinitiators, which are obtained by reaction of .alpha.,.omega.-aminopropylpolydimethylsiloxanes with 4,4'-azobis(4-cyanopentanoyl chloride), and subsequent block polymerization with vinyl monomers, is described in the Journal of Polymer Science, Volume 26, 1077-92 (1988).
One possibility for the preparation of graft copolymers comprises grafting a polymer which carries a functional end group capable of reaction onto another polymer. This process, called the "grafting onto" process, is prior art for the preparation of graft copolymers from an organosilicon polymer (core) component and an organic polymer (shell) component, as described in U.S. Pat. No. 5,223,586. In this process, (mono)olefinically unsaturated monomers which can be polymerized by free radicals, such as vinyl monomers, are grafted onto an emulsified organopolysiloxane by the emulsion polymerization process in the presence of external free radical initiators.
Homopolymerization of the organic monomers is started by this "grafting onto" process by means of an external redox initiator system, and the growing organic polymer chains bond to the (silicone) grafting basis in this procedure. An obvious disadvantage of this process is that the bonding of the organic polymer to the polysiloxane does not necessarily occur, and a considerable portion of the organic polymer is thus not grafted onto the polysiloxane, but is present as non-bonded homopolymer; this can be demonstrated by extractions on insoluble graft copolymers consisting of an organosilicon and an organic polymer content, which have been prepared by the "grafting onto" process. A further disadvantage of the "grafting onto" process is that because of intramolecular linkages, in particular loopings by multiple bonding of the organic polymer chain on the organosilicon polymer core, graft copolymers built up in an uncontrolled manner are formed, which can be demonstrated by structural characterization of such graft copolymers, for example by means of static and dynamic light scattering.
Therefore, it is the object of this invention to provide organopolysiloxanes as free radical macroinitiators with which, graft copolymers can be prepared from crosslinked organopolysiloxanes and organic polymers. These graft copolymers do not have the above mentioned disadvantages of the known graft copolymers, that is a high content of organic polymer homopolymer and an uncontrolled build-up.